1. Field of the Invention
The present invention relates to a tunnel junction structure used as a tunnel junction sensor in a magnetic head and more particularly to a tunnel junction sensor with FeX as the ferromagnetic layers.
2. Description of the Related Art
A read head employing a read sensor may be combined with an inductive write head to form a combined magnetic head. In a magnetic disk drive, an air bearing surface (ABS) of the combined magnetic head is supported adjacent a rotating disk to write information on or read information from the disk. Information is written to the rotating disk by magnetic fields which fringe across a gap between the first and second pole pieces of the write head. In a read mode, the resistance of the read sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a current is conducted through the read sensor, resistance changes cause potential changes that are detected and processed as playback signals in processing circuitry.
A read sensor is employed by a magnetic head for sensing magnetic fields from moving magnetic media, such as a magnetic disk or a magnetic tape. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. The magnetization of the pinned layer is pinned 90.degree. to the magnetization of the free layer and the magnetization of the free layer is free to respond to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
One type of read sensor employs a tunnel junction sensor. The tunnel junction sensor is a device comprised of two ferromagnetic layers (i.e., the pinned and free layers) separated by a thin insulating spacer layer and is based on the phenomenon of spin-polarized electron tunneling. The typical tunnel junction sensor uses free and pinned layers, such as NiFe or CoFe, with a spacer layer therebetween that is thin enough that quantum mechanical tunneling occurs between the free and pinned layers. The tunneling phenomenon is electron spin dependent, making the magnetic response of the tunnel junction sensor a function of the relative orientations and spin polarization of the conduction electrons between the free and pinned layers. The details of tunnel junction structures have been described in the commonly assigned U.S. Pat. No. 5,650,958 to Gallagher et al., which is incorporated by reference herein.
While it is known that ferromagnetic metals, such as CoFe, provide high Tunnel Magnetoresistance Ratio (TMR) due to their high spin polarization, it is also known that spin polarization of ferromagnetic metals is proportional to their magnetic moments (M.sub.S). These ferromagnetic metals are not a suitable metal for tunnel junction head applications due to their high coercivity (H.sub.C). Cobalt iron (CoFe) has a M.sub.S of 1400-1600 emu/cc, depending on the composition of the material, and a H.sub.C greater than 20 Oe.
From the above it becomes apparent that what is needed is a material for use as pinned and free layers in a tunnel junction structure having high saturation flux density with low coercivity.